1. Field of the Invention
The present invention relates to a display device which can display a three-dimensional image, the display device including a mask and a display unit. Particularly it relates to a three-dimensional display device which includes a display unit having non-display portions for partitioning pixels and which can display a three-dimensional image.
2. Background Art
The technology for displaying a three-dimensional image can be classified by various methods. Generally, the technology is classified into a binocular parallax method using parallax between two eyes and a spatial image reproduction method that can form a spatial image actually.
The binocular parallax method is further classified into a binocular technique and a multi-view technique. The binocular technique is a method in which an image for the left eye and an image for the right eye are obtained at two recording points corresponding to the left and right eyes respectively so that the images can be viewed by the left and right eyes respectively. In comparison with the binocular technique, the multi-view technique is a method using a larger number of recording points.
The spatial image reproduction method is further classified into a holography technique and an integral photography technique (hereinafter referred to as IP technique). Although the IP technique may be often included in the binocular parallax method, the ideal IP technique must be included in the spatial image reproduction method. That is, in the IP technique, the path of light rays at the time of reproduction is quite reverse to the path of light rays at the time of photographing. Accordingly, in the IP technique in which the number of light rays can be made sufficiently large, a perfect three-dimensional image can be reproduced in a space. Incidentally, in the IP technique, a light ray group projected from the element image goes through an exit pupil, thereby defines a projection direction, to reproduce an three-dimensional image. The IP technique in which an photograph for printing an element image is replaced by an electronic display device such as a liquid crystal device (hereinafter referred to as LCD) is also called integral imaging technique (II technique) or integral videography technique (IV technique).
For the three-dimensional image display device such as the multi-view technique or the IP technique in which a three-dimensional image can be displayed without spectacles, a three-dimensional image display device using the following configuration will be taken as an example. That is, a display panel has a plurality of two-dimensional image display pixels arranged two-dimensionally, and a three-dimensional image display pixel is configured by the plurality of two-dimensional image display pixels. Three-dimensional image display pixel data are given to the two-dimensional image display pixels respectively to thereby display the element image on the three-dimensional image display pixels. A mask is disposed on the front surface of the display panel. The mask has windows which are far smaller in size than the three-dimensional pixels and typically nearly equal in size to the two-dimensional image display pixels and which are disposed so as to correspond to the three-dimensional image display pixels.
According to this configuration, most of the element images displayed by the three-dimensional image display pixels respectively are blocked by the mask, so that only light rays transmitted through the windows can be visually recognized by the observer. Accordingly, two-dimensional image display pixels visually recognized through a certain window can be changed in accordance with the position of observation, so that a three-dimensional image can be observed by the observer. With the naked eyes.
When this configuration is applied to the multi-view or binocular technique, it is however known that there occurs display inhibition supposed to be caused by non-display portions of the plurality of two-dimensional image display pixels arranged two-dimensionally. The non-display portions include regions in which a black matrix (BM) for covering wiring and switching device portions is formed in the LCD, and outer circumferential portions of regions in which respective LEDs are formed in the LCD. Display inhibition caused by the non-display portions will be described below.
The binocular technique is a three-dimensional image display technique that can be performed on the assumption that the position of observation is far by a viewing distance L from the display surface. In the binocular technique, it is designed so that two-dimensional images produced by perspective projection at two recording points are visually recognized by the right and left eyes far by the observation viewing distance (hereinafter referred to as viewing distance) L so as to be observed as a three-dimensional image by the binocular parallax. That is, it is designed so that each of the principal beams of the light rays to display three-dimensional images is focused on the pair of converging points on a plane far by the viewing distance L from the three-dimensional image, the two focus points are separated by an eye separation distance horizontally. According to this design, different images, that is, two-dimensional images produced at two photograph positions can be viewed at the position far by the viewing distance L from the display surface, by the observer's right and left eyes respectively without use of spectacles.
The multi-view technique can be conceived to be on extension of the binocular technique. In the multi-view technique, two or more pairs of converging points corresponding to the right and left eyes are set in a plane far from by the viewing distance L from the display surface. Moreover, the three-dimensional image display device is designed so that display light rays for displaying two-dimensional images produced by perspective projection at two or more pairs of corresponding observation positions are focused on the two or more pairs of converging points. According to this design, different images (two-dimensional images produced at each pair of photograph positions) can be viewed at the position far by the viewing distance L from the display surface, by the observer's right and left eyes respectively without use of spectacles. In addition, the image observed by the left eye and the image observed by the right eye can be exchanged with each other as the position of observation is moved to the left and/or right. Accordingly, the observer can confirm change in the three-dimensional image in accordance with the movement of the position of observation.
That is, in the binocular or multi-view technique, lines connecting the centers of a number (n; n≧2) of two-dimensional image display pixels arranged two-dimensionally to the center of each window are designed to cross one another on n converging points at a viewing distance. According to such design, corresponding two-dimensional image display pixels can be visually recognized when the eyes are located on the converging points. However, the positions where lines connecting the windows to boundaries between the plurality of two-dimensional image display pixels arranged two-dimensionally cross one another are inevitably generated between these converging points. There is a problem that non-display portions are visually recognized, i.e., luminance of the three-dimensional image becomes lower, when the eyes are located on such places.
As measures to solve this problem, two methods have been proposed in JP2000-102039(kokai) and JP7-5420(kokai). One is a method in which the horizontal pitch of windows (apertures) on one line is shifted by a value not smaller than a predetermined value decided on the basis of the horizontal pitch of three-dimensional image display pixels as disclosed in JP2000-102039(kokai). The other is a method in which the horizontal positions of windows with respect to the two-dimensional image display pixels on vertically adjacent regions on a display surface of the three-dimensional image display device are shifted by near ½ or near ⅓ as large as the horizontal pitch (hp_h) of two-dimensional image display pixels (JP7-5420(kokai), JP7-322305(kokai), JP2000-102039(kokai), JP7-15752(kokai), JP10-336706(kokai), JP9-96777(kokai), JP9-22006(kokai), and JP-T-10-505689 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)). The term “near ½ or near ⅓” is, strictly, used here because the shift value needs to be slightly smaller than ½ or ⅓ as large as the horizontal pitch hp_h because focusing at a distance L is required of the multi-view technique. According to these methods, the non-display portions can be observed evenly at respective converging points though the number of two-dimensional image display pixels in which the centers of the two-dimensional image display pixels can be observed from the respective converging points at the viewing distance L is reduced to ½ or ⅓. More specifically, the number of focused lines among lines connecting the centers of the two-dimensional image display pixels to the centers of the windows is reduced to 1/m. The converging points increases to m times as the number of focused lines decreases to 1/m.
In this method, it is however necessary to control the horizontal numerical aperture of two-dimensional image display pixels strictly. The horizontal numerical aperture is defined as a horizontal width of the part which light is projected or penetrates divided by hp_h. When, for example, a lens array having, as apertures, lenses designed for totally focusing light rays on the two-dimensional image display pixels is used as a mask so that the converging points are designed to increase to m times instead of reduction in resolution of the two-dimensional image display pixels to 1/m, it is necessary to control the horizontal numerical aperture width of the two-dimensional image display pixels to 1/m times hp_h. This thing has been described in detail in JP7-5420(kokai), JP10-336706(kokai), JP9-22006(kokai), and JP-T-10-505689. If the horizontal numerical aperture is set to be larger than this value, a region in which two-dimensional images observed among respective converging points overlap one another is generated to cause a problem that luminance in this region on the display surface increases as well as this region deteriorates an image quality of the three-dimensional image (generation of crosstalk). Although JP-T-10-505689 asserts that continuous motion parallax can be obtained, this assertion is correct on the assumption that parallactic images correlate closely with one another because the quantity of projection is small, that is, on the assumption that the difference between parallactic images is small. If the correlation between parallactic images is reduced because of increase in the quantity of projection, the parallactic images are visually recognized as double images. If the horizontal numerical aperture width is set to be smaller than 1/m times hp_h, the region in which only boundaries between the plurality of two-dimensional image display pixels arranged two-dimensionally is generated again at intervals of a pitch 1/m as large as the conventional pitch. The problem that only the non-display portions are observed occurs again when the eyes are located on this region. That is, the meaning of the design to increase the converging points to m times is eliminated (JP10-336706(kokai) and JP-T-10-5055689).
The above description can be summarized as follows. In use of a lens array in which a focusing plane corresponds to the display unit as a mask, inhibition of stereoscopic view or variation in luminance occurs when the observer's head moves laterally if the horizontal numerical aperture is not strictly controlled to 1/m times hp_h. On the other hand, in use of lenses or windows, it is necessary to control the horizontal numerical aperture of the lenses or windows strictly in addition to the horizontal numerical aperture of the two-dimensional image display pixels. It is actually difficult to perform controlling in consideration of the diffraction effect of the lenses or windows. Even in the case where controlling can be made, variation in luminance at a distance out of the viewing distance is unavoidable. Because the shape of each window in the display unit is optimized individually on the basis of the display unit per se, it is undesirable from the point of view of production that the degree of freedom on design is lowered because of the problem peculiar to the three-dimensional display device. Moreover, the horizontal directions are discussed above, however, a three-dimensional image display device which gives parallax information also in the vertical directions includes a lens array having lens effects also in the vertical directions or a pinhole plate having pinholes spaced vertically. In this case, an luminance variation occurs due to the non-display portions in the vertical directions.